As both infringement and validity issues are often involved in patent infringement cases, a consistent interpretation of the technical features of the claims under dispute is critical. For a patentee, having a sufficiently broad claim scope to assert infringement is as important as a sufficiently narrow claim scope to distinguish the invention from the prior art. To achieve this goal, the patentee needs to properly utilise both claim construction and post-grant claim amendments to patent claims.

Regarding claim construction, it is generally accepted that intrinsic evidence serves as a crucial basis for interpreting patent claims. Such evidence can include descriptions in the specification and the prosecution history file (including the applicant's responses and amendments made during patent prosecution and post-grant amendments made during an invalidation procedure). However, in an infringement action, the court may not necessarily construe the claims of the patent concerned in a more limited manner based on the patentee's statements relating to adding limitations to the claim scope during prosecution or invalidation proceedings.

This was exemplified in a recent Intellectual Property and Commercial Court judgment of a patent litigation action based on a lock design.(1)


According to requests from both parties, the Court proceeded to interpret two recited technical features of the patent claim – specifically, a "cavity" and a "blocking element", combined with "filling up the cavity's remaining space not occupied by the blocking element".

The patentee intended the shape of the cavity to be interpreted as "trapezoid" based on the title of the patent (ie, "Safety Lock with Trapezoidal Safety Slot") as well as statements in response to the Patent Office during prosecution.

In the judgment, regarding claim construction the Court stated at first as follows:

The patent claims shall be interpreted with reference to the descriptions of the embodiments and drawings of the patent and in the broadest reasonable manner. Unless the specification has expressly indicated that the claim scope should be limited to the disclosures of the embodiments and drawings, the embodiments or drawings shall not be used to restrict the claim scope and hence unduly alter the scope of the claims which should have been understood by the public through reading the patent claims published by the Patent Office. (Emphasis added.)

In response to the patentee's argument on the basis of the limited interpretation made in the prosecution proceedings, the Court held that:

Claim 1 of the patent in dispute does not limit the cavity to 'trapezoid' shape because the claim only describes the cavity in the manner that 'the frontend area is provided with an insertable cavity . . . the cavity has an opening . . . the interior of the cavity is larger than the opening of the cavity'.

The Court seemed to opine that the claim wording was sufficiently clear and thus there was no need to add "trapezoid" to limit the shape of the cavity. According to the disclosure of the specification of the patent in dispute, the Court concluded that the patent in dispute had no intention to limit the cavity to a trapezoid shape, as there were embodiments of other shapes. The Court further mentioned in the judgment that the patentee did not apply for an amendment in the prosecution proceedings, even though the patentee stated in a response to the office action that "the interior of the cavity is larger than the opening of the cavity (i.e. a trapezoid)" (emphasis added). In addition, the Patent Office neither invoked any claim interpretation during examination, nor interpreted the cavity as "trapezoidal" when granting the patent. Since the claims and specification had thus been recognised as sufficiently clear, the Court held that the patentee's statement in the response to the office action alone was insufficient to support the patentee's request to limit the literal scope of "cavity" to "trapezoid".

As for the technical feature of the "blocking element" and "filling up the cavity's remaining space not occupied by the blocking element", the patentee emphasised that it was stated in the response to the office action that "the blocking element (60) and the sliding pin (70) fill up the entire cavity in the locked state", and thus "filling up" referred to a state in which the remaining space of the cavity was "completely filled up".

In this regard, the Court held that, based on the disclosure of the specification, the blocking element need only "substantially fill up the cavity" so that the blocking element remained fixed in the cavity opening, and that it was not necessary to completely fill the cavity's remaining space. The Court emphasised as follows:

Although the patentee made a statement in the response regarding completely filling up the cavity, there was no request for amendment to the scope of the claims, nor did the Patent Office's examination opinion invoke any claim interpretation during the examination. Since the claims and specification have thus been recognized as sufficiently clear, it is not necessary to limit the scope of the claims merely in response to patentee statements made during the patent prosecution.


A patentee's limited interpretation of claims, as recorded in prosecution history (eg, a response to an office action or a defence brief submitted in an invalidation procedure), is not considered sufficient to influence the court's interpretation of claims narrower than a reasonably comprehensible scope if the literal meaning of the claims is sufficiently clear and the patent specification does not provide a specific interpretation or limitation for a technical feature in the claims. Further evidence, such as Patent Office records granting the patent mainly because it accepted the patentee's limited interpretation, may be necessary. Therefore, if a patent applicant or a patentee needs a narrower claim scope to distinguish an invention from prior art, a reliable solution is to file a request for amendment or post-grant amendment to the claims, if amendment is possible, rather than merely proposing a limited interpretation in response to the Patent Office.

For further information on this topic please contact May Chen at Lee and Li Attorneys at Law by telephone (+886 2 2763 8000) or email ([email protected]). The Lee and Li Attorneys at Law website can be accessed at


(1) Judgment No. 109 Civil Patent Appeal 39.